hard to do outpatient only, since people usually want you to share in the call...and thus the pain 🙂
The closest you might be able to get would be the VA, but then you'd still have to attend on the wards, but would have house staff and fellows below you to cushion you from some of the pain.
If you want a mostly all outpatient specialty it would be better to do endocrine or rheumatology.